Previously, there has been widely performed a method of inserting bristles into bristles setting holes and fixing them by anchoring a metal plate. This method enables the brush to be simple. However, the following problems, among other problems, occur: the anchoring metal plate may become corroded; the anchoring metal plate has to be removed from plastic (the main part of a toothbrush) during disposal of the toothbrush; a thickness of a bristles implanting portion of a toothbrush cannot be reduced; bristles having large diameters cannot be implanted on the bristle implanting portion; and oblique implanting of bristles is difficult.
The following three methods do not use an anchoring metal plate:
(1) Type I: Japanese Patent Publication No. 6-16725, U.S. Pat. No. 4,635,313
The bristles are inserted into bristles insertion holes of a metal mold, and a plastic material is charged into roots of the bristles. Accordingly, a handle portion and bristles implanting portion of a toothbrush are manufactured. In this method, the plastic material tends to leak from the bristles insertion holes when charging the plastic material. In order to avoid the leakage, the roots of the bristles are fused to fill fine gaps in the bristles insertion holes. However, this is not sufficient to solve the leakage problem. When molding pressure is increased, the leakage still occurs.
(2) Type II: U.S. Pat. No. 5,458,400, Japanese Patent Application Laid-Open No. 9-182632
A toothbrush consisting of a brush head having perforated bristles setting holes and a recess, a brush neck, and brush handle is produced by injection molding from a suitable plastic material in a mold. Bristles are inserted into the perforated bristles setting holes and the ends of the bristles projecting from the back surface of the brush head are fused in an appropriate manner. The brush head portion is set in the mold to fill the brush head recess with a plastic material. In this method, leakage of the plastic material from the gap of the bristles setting holes is generated during the filling process, as in type I manufacturing mentioned above.
(3) Type III: Japanese Patent Publication No. 6-46962
The ends of the bristles are fused to form thick portions. A first surface of the head portion is also fused. The thick portions of the bristles are pressed against the fused surface of the head portion to fix the bristles to the head portion. In this method, quality control is difficult.
Recently, there is desired a toothbrush which is excellent for dental health, has good plaque removing characteristics, has excellent interdental cleaning characteristics, and is effective at massaging gums. In order to manufacture such a toothbrush, various creative efforts have been applied to the handle and the bristle implanting portion. The present invention relates to an improvement of the bristle implanting method.
Bristle performance depends upon the bristle implanting method, and recently various methods have been tried. Apart from the bristles implanting method, there are several factors to be considered for good performance of toothbrush. These factors include: a strength of the bristles, a size of the bristles, a thickness of the bristles, an area and a shape of the bristles setting holes, and the like. It is desirable that a single apparatus may manufacture various types of toothbrushes.
The following items can be listed as main factors of the bristles implanting method for a toothbrush.
(1) An angle of bristles against the brush head can be freely altered.
(2) A shape of bristles use ends can be optionally designed.
(3) A brush head can be made thin.
(4) No leakage of plastic material exists near bristles setting holes.
(5) Equipment of compact size and wide adaptability for production of several kinds of toothbrushes.
The present invention intends to manufacture a toothbrush satisfying the factors mentioned above without using an anchoring metal plate.
In a toothbrush without an anchoring metal plate, the oblique bristles implanting technique is difficult. A toothbrush having an inclined bristles is disclosed, for example, in WO99/23910A1, WO01/13762A1 and WO01/14117A1. The manufacturing method in these references falls within the method the type I described in the background art. In this method, in order to prevent a leakage of the charged plastic material from the bristles insertion hole; two methods are employed, i) increasing a charging density of the bristles, and ii) filling the bristles insertion hole with plastic material. Since the bristles implanting base portion of the toothbrush becomes exposed when used, the method ii) mentioned above is difficult to employ. Accordingly, the method i) mentioned above may be employed, however, in the case of using precut bristles, it is hard to insert the bristles into the bristles insertion hole at a high density.
Japanese Patent Application Laid-Open No. 9-182632 discloses that the bristles are inserted into the bristles insertion hole from a tapered holder by a bristles extrusion pin. However, all of the bristles are not inclined with respect to the implanted bristles base portion.
U.S. Pat. No. 4,693,519 and U.S. Pat. No. 4,255,224 disclose oblique implanting of bristles. However, these methods do not attain implanting with constant number and high density of bristles. Accordingly, in these methods a gap in the bristles insertion hole tends to be formed and the leakage problem is not resolved. Further, these methods do not include a method to change the shape of the use end of the bristles.
In order to pick up a constant number of the bristles into the bristles insertion hole and implant the bristles with a high density, it is well known to insert from a reel. Japanese Patent Application Laid-Open No. 7-194433 discloses a method of supplying the bristles from the reel, cutting the bristles to a suitable length, and thereafter increasing an implanting charging density of the bristles and forming the use end of the bristles. This method requires a compression apparatus and makes the equipment structure complex. Further, formation of the use end shape of the bristles is limited. It is possible to apply this method to oblique implanting of bristles. However, it is necessary to arrange a reel for supplying the bristles in an oblique direction. Accordingly, a direction of the implanting (a direction of the incline) is limited in view of contact and intersection between the reels and conveying paths of the bristles.